1. Field of the Invention
The present invention relates to a high voltage switch device, and a multi-pass image forming apparatus having the same. More particularly, the present invention relates to a high voltage switch device that selectively supplies high current to a plurality of devaluing units, and a multi-pass image forming apparatus having the high voltage switch device.
2. Description of the Related Art
Generally, an electrophotographic color image forming apparatus forms a color mage by forming an electrostatic latent image on a photosensitive medium charged with a uniform electric potential by emitting a beam onto the photosensitive medium. The electrostatic image is developed with a toner of a predetermined color, and transferred and fixed onto print paper. Toner colors generally used in the color image forming apparatus are yellow (Y), magenta (M), cyan (C), and black (K). Therefore, to adhere the four toner colors on the electrostatic latent image, four developing units are required. A high voltage (that is, over hundreds to thousands of volts)for developing bias for adhering the toners onto the photosensitive medium and for supply bias for supplying the toner to the developing rollers are supplied to the developing units.
Methods of forming a color image include a single path method in which four exposure units and four photosensitive mediums are used, and a multi-pass method in which a single exposure unit and a single photosensitive medium are used. A color image forming apparatus adopting the single pass method takes approximately the same time for color printing and black and white printing, and, thus, is usually used in a high-speed color image forming apparatus. However, because it has four exposure units and four photosensitive mediums, the price of the color image forming apparatus adopting the single pass method is high. Thus, a color image forming apparatus operating in a relatively low speed includes a single photosensitive medium and a single exposure unit and adopts the multi-pass method in which exposing, developing, and image transferring are repeatedly performed for each of the colors to form a color image on an intermediary medium and to transfer the color image onto print paper.
In an image forming apparatus using the multi-pass method, the four developing units operate sequentially. Thus, a device for sequentially transmitting the rotation force of a driving motor to the four developing units is required. A multi-pass image forming apparatus is desired, such as for inkjet printers for small office and home office (SOHO) use, as well as for color image forming apparatuses for home use. Thus, miniaturization and low cost of the multi-pass image forming apparatus are important. A conventional high voltage switch device selectively connects four switches using four axial type solenoids. The conventional high voltage switch device is expensive and large. Additionally, when the solenoid is turned “on,” heat is generated, thereby reducing durability.
Accordingly, a need exists for an improved high voltage switch device that reliably controls high-voltage current transmitted to a developing unit of a multi-pass image forming apparatus.